A while back I had a 426YZF set up for trails. Then I added a KLR. The 426 sat unused while I played on the KLR. I decided I liked this dual sport stuff so I sold both and got a KTM 640 Adv. Rode that for awhile, sold it and got my '07 990 Adv. Each bike was more fun than the last.
I'm looking to trade my 990 Adventure for an SMT but that's just because I'm getting too old to ride enough dirt to need the Adventure. Other than a SMT I don't see anything I would want instead. This is the first time since the early 1960s that I can't find another bike that I just "gotta" have.
Don't know first hand whether or not to recommend the F800GS.
I DO know first hand that if you had fun on the KLR, it'll take a chisel to get the grin off of your face riding a 990.
Good riding & have fun either way.
Horsepower determines how fast you hit the wall. Torque determines the size of the hole you make.